1. Field of the Invention
The present invention relates to a full-closed control apparatus for performing position control based on a position signal of a load driven by a motor.
2. Description of the Related Art
Generally, full-closed control for performing speed control based on a speed signal of a motor and performing position control based on a position signal of a load driven by the motor is required for accurate positioning. If rigidity in coupling the motor and the load to each other is low, it is however impossible to achieve high-speed control by ordinary full-closed control. This is because a control system vibrates at a frequency near an antiresonance frequency of a mechanical system when the gain of a position controller is increased, that is, because the upper limit of the gain of the position controller becomes lower than that in semi-closed control. To solve this problem, the present applicant has proposed a full-closed control apparatus shown in FIG. 5 in Japanese Patent OPI publication No. 2001-309676.
In FIG. 5, the reference numeral 1 designates a motor-including mechanical system which has an equivalent rigid model 5, a mechanical resonance system 6, a load principal vibration system 7, and an integration 8. Incidentally, J is inertia of a movable portion of the mechanical system, D is a coefficient of viscous friction of an equivalent rigid system, xcfx89r is an angular frequency of resonance, xcex6r is a viscosity coefficient of resonance, xcfx89a is an angular frequency of antiresonance, and xcex6a is a viscosity coefficient of antiresonance. The reference numeral 2 designates a load vibration suppression compensator which has an amplitude adjuster 9, and a band-pass filter 10. The reference numeral 3 designates a position controller. The reference numeral 4 designates a speed controller. A difference signal EL obtained by subtracting a load position signal XL from a position command Xr is multiplied by a position control gain Kp to thereby obtain a speed command basic signal Vrb. A difference signal obtained by subtracting a speed command Vr from a load speed signal VL is input into the band-pass filter 10. An output of the band-pass filter 10 is input into the amplitude adjuster 9. A signal obtained by adding a speed command compensatory signal Vrh as an output of the amplitude adjuster 9 to the speed command basic signal Vrb is set as a new speed command Vr. A difference signal obtained by subtracting a motor speed Vm from the speed command Vr is input into the speed controller 4. An output of the speed controller 4 is set as a torque command Tr. The motor-including mechanical system 1 is driven on the basis of Tr.
In the related art, if the gain of the speed controller is sufficiently high, the gain of the equivalent rigid system speed loop model is approximately equal to 1 in a low-frequency region. Accordingly, the difference signal VLd obtained by subtracting the speed command Vr from the load speed VL can be regarded as an estimated signal of vibration contained in the load speed. When VLd is phase-adjusted by the band-pass filter and gain-adjusted by the amplitude adjuster to cancel a vibration mode contained in the speed command basic signal, a position loop can be stabilized even in the case where the gain of the position controller is high.
In the related art, however, if the gain of the speed controller cannot be increased so sufficiently, the gain of the equivalent rigid system speed loop model is lower than 1 in a low-frequency region. For this reason, a low-frequency component is contained in the difference signal VLd obtained by subtracting the speed command Vx from the load speed VL. On the other hand, because the band-pass filter is also used as a phase adjuster, a predetermined phase delay is given to the oscillation frequency fd of the position loop. Accordingly, the center frequency fo of the pass band in the band-pass filter becomes lower than the oscillation frequency fd of the position loop. When, for example, the band-pass filter is constituted by a combination of a two-stage low-pass filter (1/(1+Tfs)) and a two-stage high-pass filter (Tfs/(1+TfS)) in the case where the oscillation frequency fa of the position loop is 40 Hz, the center frequency fo of the pass band in the band-pass filter is 16.6 Hz (FIG. 6) because a phase delay of 90xc2x0 is given to a point of 40 Hz.
Because the speed command compensatory signal Vrh contains a low-frequency component with a large amplitude as described above, there is a problem that low-frequency vibration or overshooting is apt to occur (FIG. 8).
Therefore, an object of the invention is to provide an apparatus by which the problem in the related art can be solved and by which while the vibration of a position loop can be suppressed, the position control gain can be increased to achieve speedy and accurate positioning.
To achieve the foregoing object, the invention provides a full-closed control apparatus for performing speed control based on a speed signal of a motor and performing position control based on a position signal of a load driven by the motor, including: an equivalent rigid system speed loop model; a band-pass filter; an amplitude adjuster; and a unit for inputting a speed command of a speed control loop into the equivalent rigid system speed loop model, inputting a difference signal obtained by subtracting an output of the equivalent rigid system speed loop model from a speed signal of the load into the band-pass filter, inputting an output of the band-pass filter into the amplitude adjuster and outputting a signal obtained by adding an output of the amplitude adjuster to an output of a position controller, as a new speed command.
The invention also provides a full-closed control apparatus for performing speed control based on a speed signal of a motor and performing position control based on a position signal of a load driven by the motor, including: an all-pass filter; a band-pass filter; an amplitude adjuster; and a unit for inputting a difference signal obtained by subtracting a speed command of a speed control loop from a speed signal of the load into the all-pass filter, inputting an output of the all-pass filter into the band-pass filter, inputting an output of the band-pass filter into the amplitude adjuster and outputting a signal obtained by adding an output of the amplitude adjuster to an output of a position controller, as a new speed command.
The invention further provides a full-closed control apparatus for performing speed control based on a speed signal of a motor and performing position control based on a position signal of a load driven by the motor, including: an equivalent rigid system speed loop model; an all-pass filter; a band-pass filter; an amplitude adjuster; and a unit for inputting a speed command of a speed control loop into the equivalent rigid system speed loop model, inputting a difference signal obtained by subtracting an output of the equivalent rigid system speed loop model from a speed signal of the load into the all-pass filter, inputting an output of the all-pass filter into the band-pass filter, inputting an output of the band-pass filter into the amplitude adjuster and outputting a signal obtained by adding an output of the amplitude adjuster to an output of a position controller, as a new speed command.